Collaborative Research: Emergent Mechanics of Randomly Packed Elastic Filaments

合作研究：随机填充弹性丝的新兴力学

• 批准号: 1825924
• 负责人: Hunter King
• 金额: $ 26.3万
• 依托单位: University of Akron
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2018
• 资助国家: 美国
• 起止时间: 2018-09-01 至 2022-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1825924&HistoricalAwards=false
• 关键词: Collaborative; Research; Emergent; Mechanics; Randomly

When a cardinal builds her iconic cup-nest, she uses her own body as template and molds thin twigs, grass strands, and bark strips into a structure that, despite its softness, reliably holds its shape against various mechanical perturbations. This naturally-selected engineering solution is the result of a subtle interplay between geometry, elasticity, and friction that has not yet been characterized or modeled despite its potential in building, packaging, self-repairing, shock-absorption, and material reusability. The 'bird nest', if defined as a random packing of slender, elastic elements, is an unusual material: it is cohesive without attractive interactions; it is collectively soft and plastic while its elements are hard and elastic. Through coordinated physical and computational experiments, this collaborative project will advance the science of soft granular materials by relating bulk mechanical properties of idealized 'nest systems' with variations in constituents' properties and geometry. Results will generate new knowledge in granular physics, and will appeal to emerging aleatory architecture and engineering paradigms. Indeed, the ability to build through impermanent contacts and design lightweight materials with prescriptive mechanical properties cuts through many areas of high current importance: civil engineering and architectures (reliable, inexpensive, reusable and self-repairing materials), transportation (lightweight composites, shock absorbers), advanced manufacturing. This is in line with the national need of increasing industry competitiveness, which advances the national health, prosperity, and welfare; and secures the national defense. The project also promises to capture the imagination of a broad audience by creating an unusual bridge between relatable protagonists (birds) and often inaccessible fields of physics and engineering. Additionally, STEM outreach activities will be conducted at individual institutions to attract middle school students and female students, respectively, towards science and engineering. Undergraduate students will also be offered positions in either group for exposure to advance engineering research.With increasing aspect ratio, the mechanical behavior of disordered granular packings changes. Where applied stresses distribute in chains of 1D contacts for spheroids, slenderness introduces bending moments and long-range interaction. Impermanent frictional contacts set the system apart from semi-flexible polymer networks and other non-woven materials which derive mechanical response from permanent crosslinks. Experimental evidence from disordered, randomly packed, elastic fibers or filaments based structures, such as the bird nests, suggest that these material systems exhibit frequency-dependent elastoplastic behavior, finite tensile response, and enhanced specific strength. In the absence of a theoretical framework and strictly applicable principles of statistical mechanics, an experimental platform for the benchmarking and physical characterization of these materials will be developed in this project. These will be complemented by a high fidelity computational counterpart to direct a search for novel mechanical states and transitions. The project will provide insights into the relationship between macroscopic and microscopic mechanics of bird nest-like systems, paving the way towards prescriptive design of novel materials. Moreover, it will spur new directions in granular physics theory and explain a functional mechanism from a naturally-selected engineered structure.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

当红雀建造她标志性的杯巢时，她会用自己的身体作为模板，将细树枝、草丝和树皮条塑造成一个结构，尽管它很柔软，但在各种机械扰动下仍能可靠地保持其形状。这种自然选择的工程解决方案是几何形状、弹性和摩擦之间微妙相互作用的结果，尽管它在建筑、包装、自我修复、减震和材料可重复利用方面具有潜力，但尚未对其进行表征或建模。如果将“鸟巢”定义为细长弹性元件的随机堆积，那么它是一种不寻常的材料：它具有粘性，但没有吸引力的相互作用；它总体上是软的和可塑的，而其元素是硬的和有弹性的。 通过协调的物理和计算实验，该合作项目将通过将理想化“巢系统”的整体机械性能与成分性能和几何形状的变化联系起来，推进软颗粒材料的科学发展。结果将产生粒状物理学的新知识，并将吸引新兴的偶然架构和工程范例。事实上，通过非永久性接触进行建造和设计具有规定机械性能的轻质材料的能力突破了当前重要的许多领域：土木工程和建筑（可靠、廉价、可重复使用和自我修复的材料）、交通运输（轻质复合材料、减震器） ）、先进制造。这符合国家提高产业竞争力的需要，促进国民健康、繁荣和福利；并确保国防。该项目还承诺通过在相关的主角（鸟类）和通常难以进入的物理和工程学领域之间建立一座不寻常的桥梁，来吸引广大观众的想象力。此外，还将在各个机构开展 STEM 推广活动，以分别吸引中学生和女学生学习科学和工程。本科生还将获得任一组的职位，以接触先进的工程研究。随着长径比的增加，无序颗粒填料的机械行为会发生变化。当施加的应力分布在球体的一维接触链中时，细长会引入弯矩和长程相互作用。永久摩擦接触使该系统有别于半柔性聚合物网络和其他非织造材料，后者从永久交联中产生机械响应。来自无序、随机堆积、弹性纤维或长丝结构（例如鸟巢）的实验证据表明，这些材料系统表现出频率依赖性弹塑性行为、有限的拉伸响应和增强的比强度。 由于缺乏统计力学的理论框架和严格适用的原理，该项目将开发一个用于这些材料的基准测试和物理表征的实验平台。 这些将得到高保真计算对应物的补充，以指导寻找新颖的机械状态和转变。该项目将深入了解鸟巢状系统的宏观和微观力学之间的关系，为新型材料的规范设计铺平道路。 此外，它将激发颗粒物理理论的新方向，并解释自然选择的工程结构的功能机制。该奖项反映了 NSF 的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。

项目成果

Mechanics of randomly packed filaments—The “bird nest” as meta-material

随机排列的细丝的力学——作为超材料的“鸟巢”

• DOI: 10.1063/1.5132809
• 发表时间: 2020
• 期刊: Journal of Applied Physics
• 影响因子: 3.2
• 作者: Weiner, N.;Bhosale, Y.;Gazzola, M.;King, H.
• 通讯作者: King, H.

Micromechanical Origin of Plasticity and Hysteresis in Nestlike Packings

巢状填料塑性和滞后的微机械起源

• DOI: 10.1103/physrevlett.128.198003
• 发表时间: 2022
• 期刊: Physical Review Letters
• 影响因子: 8.6
• 作者: Bhosale, Yashraj;Weiner, Nicholas;Butler, Alex;Kim, Seung Hyun;Gazzola, Mattia;King, Hunter
• 通讯作者: King, Hunter